Method of assembling a flanged waveguide device



R. JIMENEZ May 31, 1955 METHOD OF ASSEMBLING A FLANGED WAVEGUIDE DEVICE Filed May 15, 1951 Fig- 4 INVENTOR I? U001 pH JMf/WEZ ATTORNEY lZa United States Patent METHOD OF ASSEMBLING A FLANGED WAVEGUIDE DEVICE Rudolph Jimenez, Schenectady, N. Y., assignor to Sylvania Electric Products Inc., a corporation of Massachusetts Application May 15, 1951, Serial No. 226,454

2 Claims. (Cl. 29--25.13)

The present invention relates to waveguide apparatus for transmission of microwave energy and, in particular, to waveguide structures containing gas at low pressure such as transmit receive (TR) and anti-transmit receive (ATR) tubes.

The main object of the present invention resides in the provision of a construction and an assembly method for locating and joining a mounting flange to the body of a waveguide portion of the device in a way that will assure accurate orientation of the face of the flange. Devices of the character here involved conventionally include a length of metal waveguide of comparatively thin wall construction, to which there is jointed a mounting flange at one end, or at both ends, and the joint is required to be vacuumtight in order that the gas contained in the device at very low pressure may be preserved against leakage and contamination. It is also required that an end closure for the waveguide be accurately oriented in relation to other structures constituting one or more discharge gaps within the waveguide. The orientation of the window relative to the discharge gap is also critical, and is influenced by the manner of mounting the flange. In the illustrative embodiment that is described in detail below, the flange is located on the waveguide exterior by means of a flat key extending all the way around the waveguide and fitting into a grove in the waveguide exterior. The key, the flange, and the waveguide are united in a hermetic joint accurately locating the face of the flange in a predetermined accurate spacing position in relation to the window, and to a pair of elec' trodes within the waveguide constituting a discharge gap. The manner of forming the waveguide and flange assembly is such as to leave the end of the waveguide accessible to receive a waveguide window and to locate that window accurately in relation to the discharge gap.

Considerable difficulty has been encountered with other' forms of assembly in achieving both the necessary and dimensional tolerances and in assuring, with a high degree of consistency in production, the necessary hermetic seals. The nature of the invention and further features of novelty will be better appreciated from the following detailed disclosure of an illustrative embodiment of the invention which is shown in the accompanying drawings, wherein:

Figure 1 is a central longitudinal cross-sectional view of a TR tube embodying features of the invention;

Figure 2 is a plan view thereof;

Figure 3 is a perspective view of the two part key employed in the device in Figures 1 and 2;

Figure 4 is a greatly enlarged detail view of the portion of the device in Figure l.

The invention is illustrated as being employed in a typical form of transmit-receive tubes which conventionally includes a mounting flange of relatively thick, rigid proportions, joined to a rectangular length of waveguide 12, forming the body of the device. Metal electrodes 16 and 18 constitute a discharge gap within the waveguide, and keep-alive electrode 20 within the electrode 18 is used to maintain a small volume of low-pressure gas in ionized condition in the region of the tips of electrodes 16 and 18. Electrodes 16 and 18 are of metal and are conductively joined to the waveguide wall. Keepalive electrode 20, though insulated from electrode 18, is joined thereto by a glass seal 22 for rigid and vacuumtight assembly to the device. Two additional gaps 16' and 18 lacking a keep-alive electrode are also provided. Associated with each discharge gap is a conventional iris 28 whose purpose is to establish resonance in combina tion with the capacitive effect of the gap electrodes. A window 24 is joined to one end of the device and a second window 26, is joined to the opposite end of the device. Each window includes a frame portion 24a, 26a, and a central glass or ceramic portion 24b, 26b, respectively.

Significantly, the flange is joined to waveguide 12 in an arrangement exposing flanges 24a and 26b to the ends of waveguide 12 whereby the windows may be accurately oriented in relation to the discharge gap established by electrodes 16 and 18 and by the irises 28.

Referring now to Figures 3 and 4, a two-part key 30, both portions identical, are formed and disposed in a groove 32 in waveguide wall 12. The scale of values involved may prove helpful for appreciation of some of the factors involved. The wall thickness of waveguide 12 is, in an example, .080" and groove 32 which completely surrounds the waveguide 12 is one-half of that thickness, or .040" deep.

In routine manufacture, apair of key portions 30 are slid into groove 32 at each end of waveguide body 12. The parts are properly dimensioned to insure butting of the ends of key portions 30 against each other in the assembly. Thereafter, flange 10 is slid over the waveguide and against the face of two-part key 30. It is readily possible to control accurately the spacing between key 30 and the end 12a of the waveguide. The separation of front and back flange surfaces 10a and 10b are also susceptible to accurate control. In this way, the key serves to locate the flange in relation to the waveguide which carries the devices constituting the discharge gap and, at the same time, it exposes the end surface 12a of the waveguide for receiving each window and locating the Windows accurately in relation to the faces of the mounting flanges.

The key shown advantageously surrounds the waveguide and, because of this feature, it is adapted to perform the further function of insuring success in forming vacuum-tight bonds between the flanges and the waveguide body, consistently in large numbers of these devices. It will be understood from the following:

If, for a moment, the question of orienting flange 10 is disregarded, and this flange were assembled to the exterior of a length of waveguide, it would be possible to locate a preform of brazing material. on the waveguide exterior against the surface 10b. By properly heating the assembly, it would be possible to join the flange to the waveguide body. There are, however, irregularities of suflicient extent inherent which produce wide differences in capillary action at different peripheral points of the waveguide surrounded and contracted by flange 10. Capillary action at some points consequently tends to deprive others entirely of brazing material with the result that leaks tend to develop in the final construction.

In contrast, when a brazing preform is assembled adjacent to key 30, with flange 10 also assembled to the waveguide body, remarkably consistent success is achieved in hydrogen-firing the assembly to form vacuum-tight joints of the key, the flange, and the waveguide. It is possible that the sharp bends in the capillary path promotes uniformity in flow of brazing material while the unit is subjected to brazing heat.

In the same heating operation, or advantageously in a subsequent operation, windows 2411 and 26a are brazed or soft-soldered in place at the ends of waveguide 12. These joints unite the window flange 24a (26a) to the ends of the waveguide. The hermetic seal is also formed be tween the window and the flange 10.

It is conceivable that isolated pins could be used extending outward from holes in waveguide 12 to constitute a shoulder for locating flange 10 on the waveguide body; but, while serving part of the desired functions, such pins would not be adequate to insure uniformity of vacuumtight seals being formed.

The window and flange assembly illustrated at the left end of Figure 1 is naturally subject to a latitude of variation and, in fact, dilferent forms of construction are shown at the opposite ends of the device. Window 26 has a cup flange 26a that is oriented in relation to the discharge gap 16, 18', by the end of the waveguide section, just the same as waveguide end 12:! orients flange 24a. A wire-braid gasket 34 is shown assembled to the right end of the device, but it will be understood that window 26, flange 10, and body 12 are hermetically sealed together in the same way as that described for window 24 and flange 10, on waveguide 12. The key in each instance serves as an abutment locating the flange accurately and promoting excellence of hermetic sealing.

The device in Figure 1 is actually a TR tube, but the invention obviously is applicable to other waveguide devices, whether having one or two flanges. Such other devices include the usual A-T-R tubes having one flange, to pre-TR tubes and to attenuator tubes. Further, it will be recognized by those skilled in the art that detailed changes in design may be made without, however, departing from the spirit of the invention and, therefore, the

appended claims should be accorded that latitude of interpretation which is consistent with the scope of the invention.

What is claimed is:

l. The method of fabricating a waveguide structure having an external flange, including the steps of forming an encircling groove in a length of waveguide, disposing an encircling key in said groove so as to project outside said groove, assembling a flange against said key and about said waveguide, and uniting said key, said waveguide and said flange.

2. The method of fabricating an electric discharge device including the steps of forming a discharge-gap structure within a length of waveguide critically spaced from an end thereof, forming a surrounding groove in said waveguide at a position accurately spaced from said waveguide end, disposing a key in said groove to surround the waveguide and project out of said groove, joining a flange to said key and said waveguide in a vacuumtight seal, and sealing a window to the inside of said flange and against said end of said waveguide.

References Cited in the file of this patent UNITED STATES PATENTS 1,397,080 Coleman Nov. 15, 1921 2,232,098 Deichman Feb. 18, 1941 2,412,997 Litton Dec. 24, 1946 2,444,303 McCarthy June 29, 1948 2,476,586 Darash July 19, 1949 2,524,268 McCarthy Oct. 3, 1950 FOREIGN PATENTS 221,075 Switzerland May 15, 1942 

